Enrichment by extragalactic first stars in the Large Magellanic Cloud

Abstract

The Large Magellanic Cloud (LMC) is the Milky Way’s most massive satellite galaxy, which only recently (~2 billion years ago) fell into our Galaxy. As stellar atmospheres preserve the composition of their natal cloud, the LMC’s recent infall makes its most ancient, metal-deficient (‘low-metallicity’) stars unique windows into early star formation and nucleosynthesis in a formerly distant region of the high-redshift universe. Here we present the elemental abundances of ten stars in the LMC with iron-to-hydrogen ratios ranging from ~1/300th to ~1/12,000th that of the Sun. Our most metal-deficient star is markedly more metal-deficient than any in the LMC with available detailed chemical abundance patterns and was probably enriched by a single extragalactic ‘first-star’ supernova. This star lacks appreciable carbon enhancement, as does our overall sample, unlike the lowest-metallicity stars in the Milky Way. This and other abundance differences affirm that the extragalactic early LMC experienced diverging enrichment processes compared to the early Milky Way. Early element production, driven by the earliest stars, thus, appears to proceed in an environment-dependent manner.